Filling fittings have been installed in order to make the tanking of vehicles easier. In the case of a system made known by WO 03/010022 A1, on the filling fitting is affixed a carrier with a square wall in which an entry opening is provided to receive a hand held pistol-nozzle for fuel injection. On the other side of carrier is a closure cover, which is pivotably set to rotate about a turning shaft transverse to the center line of the input opening, whereby, on the upper side of the closure cover is to be found a sealing element which works in conjunction with an opening rim which forms a seat for the sealing element. Further, on the upper side of the closure cover is affixed a closure component, which, in the closed position of a closure cover penetrates the inlet opening with an axial section. Carried on this axial section is a projecting closure element which extends itself radially outward. Finally, above the transverse wall is provided a supporting closure ring, which in turn carries a circumferential section, which extends itself radially inward. This acts in common with the closure elements in the manner of a screw drive or a bayonet connection, whereby the closure cover is pressed, with its sealing means, onto the underside of a transverse wall. The closure ring is so supported, that it is rotatable. Accordingly, in an initial turning position of the closure ring, the circumferential section thereof is beyond contact with the closure elements. Subsequently, in a second turning position, the circumferential section engages the closure elements from the underside. When this occurs, the closure cover with its seal, is pressed with an axial, effective force against the under side of the transverse wall.
In the case of the disclosure regarding filling fittings made by WO 03/010022, the closure ring supports itself directly on the carrier of the tank closure. So that the sealing assurance, with this arrangement, is sufficient, the requirement is, that the closure cover, or better, the plane thereof, be aligned exactly parallel to the plane of the closure ring. The same applies in the case of the counter surface of the transverse wall. When the parallelism of the components is not maintained, a danger exists, that the sealing element is not uniformly seated, but rests at an inclined angle and can circumferentially press with unequal forces against the seal seat. The result is, that no sufficient blocking means is present and fuel vapors can migrate into the surrounding atmosphere.
Even if the plane-parallelism of coacting components is assured, it can come about, that due to the action of the fuel or because of mechanical or thermal effects, that a distortion of the coacting components can occur, and this can lead especially to a swelling of the sealing element along with the therewith associated leakages. This is particularly true, if, in an aggressive manner, the swelling takes place in different circumferential sections of the sealing element. Beyond this, a completely swelled sealing element leads to an unmanageable increase of the force necessary to activate the closure ring.